There are an increasing number of medicament delivery devices on the market that are arranged with a number of different automatic functions and features. In particular automatic injection is a feature that is often provided on injectors. An automatic injection facilitates the handling of a medicament delivery device as compared to manual injection, because an injection sequence, and in particular the start, requires quite high forces. This is because of a rather high break loose force for moving the stopper. A higher force requirement is also present if the medicament has a higher viscosity and/or a narrow injection needle.
Another feature that is important and that is often automatic is the shielding of an injection needle after the medicament delivery device has been withdrawn. This is often performed by a needle guard that extends in the proximal direction by a spring or the like when the medicament delivery device is removed from the dose delivery site and surrounds the needle. In the fully extended position, the needle guard is locked by appropriate locking elements so that the needle guard cannot be pushed back into the medicament delivery device again, exposing the injection needle.
The above mentioned functions may be triggered/activated by the movement of the needle guard both when retracting into the medicament delivery device as well as extending out of the medicament delivery device. One solution that utilises these features is disclosed in document WO2011/123024A1. The medicament delivery device disclosed therein is arranged with a rotator, which is provided with guide ridges on its outer surface. These guide ridges are arranged to cooperate with protrusions on distally extending arms of a longitudinally movable needle guard such that the rotator is turned when the needle guard is moved in the distal direction during a penetration sequence. The turning of the rotator will cause a release of a plunger rod that is in a tensioned state, whereby the release will cause a dose of medicament to be expelled through a medicament delivery member. The turning of the rotator will also cause a blocking element to be positioned in line with the protrusions as seen in a longitudinal direction such that when the needle guard extends after removal of the medicament delivery device, the protrusions will pass the blocking element and lock the needle guard in the extended shielding position.
Even though this solution has its advantages, for some types of medicament delivery devices, the releasing of the tensioned plunger rod requires a separate mechanism dedicated to the holding and releasing of the plunger rod for performing an injection sequence. In those cases, the start of the injection sequence and the locking of the needle guard would be performed by separate mechanisms.